Garage door operators have been gaining in popularity and have evolved into two separate types for the majority of door operators produced in the United States. The first type is a screw drive and the second is a chain drive. The screw drive type of door operator is over 22 years old, as shown, for example, by U.S. Pat. No. 2,954,224. The screw drive type utilizes a one, two or three-start thread screw, disposed near the ceiling of the garage, and in the order of one-half inch diameter, with about 300 degrees of the screw enveloped and guided within an elongated guide rail. A partial nut is guided by the guide rail and engages the screw in the remaining exposed, about 60-degree, arcuate extent of the screw. The partial nut is connected to the garage door for establishing opening and closing movements, depending on clockwise or counterclockwise rotation of the screw.
The chain drive type of garage door operator utilizes an elongated guide channel, again disposed near the ceiling of the garage, and journaling the drive sprocket and an idler sprocket at opposite ends over which first and second runs of a link chain are trained. A carriage slides on the guide channel and is connected to one run of the chain for forward and reverse movements for opening and closing movements of the door. In the chain drive type of door operator, the guide channel for many years has been cut into two or three pieces for compactness of the shipping container and spliced together end-to-end at the garage site for use.
In order to be useful throughout the United States, both types of garage door operators must be usable with a large majority of the different types of garage doors in use. There are sectional doors of three, four, or five sections which move upwardly on a track to a position inside the garage and over the space in the garage for the automobile. Another door is a slab door of one piece which moves upwardly and outwardly to a position partially in and partially outside the garage as a canopy in a generally horizontal position. Another single slab-type door is one which moves on hardware upwardly and inwardly to a position entirely within the garage into a generally horizontal attitude. To be satisfactorily merchandised, both the screw drive and chain drive type of door operator must operate satisfactorily with at least these three different types of garage doors, and such types in a full range of common sizes.
The screw drive door operator currently enjoys the largest market share, one reason being that most of the screw is contained within the guide rail, with the slotted opening along the bottom edge for the partial nut. Therefore, lubrication of the screw may satisfactorily be provided for long life. On the other hand, the chain drive door operator is one which has the chain and sprockets relatively exposed, hence being much more subject to contamination, and therefore wear, for a more limited life. The fact that the chain drive door operator could have a rail cut into sections for a shorter package was a shipping advantage over the screw drive operator, which, until recently, was still shipped in a package about ten feet long. The doors with which both types of operator were used varied in height from 61/2 to 8 feet, so that a guide rail about 9 or 10 feet long mounted along the garage ceiling was generally required in order to be able to satisfactorily operate the great majority of garage doors installed in garages throughout the United States.
More recently, there has appeared on the market a screw drive operator, shown in U.S. Pat. No. 4,241,540, wherein the guide rail is provided with splice plates and the screw is provided with a double pivoted coupling so that the screw part and associated guide rail part may be folded upon itself for a shipping carton about half the total length of the unfolded and spliced guide rail. This shortens the length of the shipping package but introduces further problems of wear at the double pivoted coupling and shortened life of the product.
Installation of garage doors by a service man is becoming increasingly more expensive, and therefore a simplified door operator construction which may be installed by the homeowner is desirable. The average professional installer will have a truck to transport a 10-foot long package, but the average homeowner needs a shorter package so that he may take it home in the trunk of his automobile. Also, the average homeowner does not lubricate his garage door operator, not even once in five years, so a garage door operator which is troublefree without yearly lubrication is desirable.
The problem to be solved, therefore, is how to construct a garage door operator which is competitive in price, operable for a long life in relative quiet and safety without contamination of lubrication, and which may be packaged for shipping in a relatively short carton, yet which will be operable with the great majority of upward acting garage doors currently in use in the United States.